Over the past forty years, in particular, an industry has developed wherein naturally occurring sorptive minerals, and primarily the absorbent clay known as fuller's earth, have had ever-increasing uses as granular absorbents to take up undesirable accumulations of oil and grease and other liquids on the floor in factories, in machine shops, filling stations and the like. This absorbent clay in granular form has also had an ever-expanding use in pet animal toilet boxes, and especially for so-called cat boxes. A further use has been found for such absorbent clay granules as carriers for agricultural chemicals whereby pesticides, herbicides, fertilizers and the like are combined with such a carrier and distributed by various means to control weeds, pests, and the like. The porosity, and hence the absorbent property of the absorbent clays, as well as low bulk density are significant properties in the above uses for this granular clay material. The granules as used result from crushing, calcining, and screening and vary in size for the different uses, but in general, they range from those which would pass through a standard 6 mesh screen to those which are retained on a 60 mesh screen. In all of the above products made from absorbent clay such as fuller's earth, it is important that during use the granules maintain the size and condition in which they are marketed. Also, it is important that the absorbent clay granules do not turn to dust, for the dust causes objectionable dirtiness, and it spreads in the air, on persons, or on animals using the material.
Generally, the fuller's earth absorbent clay has performed a useful function in this industry which has been built around the desirable properties described above. There is a problem in utilizing fines which result from the crushing and screening of the absorbent clay to provide it in useable granule form, and such fines have been largely a waste product in the industry. The present applicant invented a process for pelletizing such fines which is covered in application Ser. No. 668,637, now U.S. Pat. No. 4,036,928 and assigned to Oil-Dri Corporation of America. This is a satisfactory utilization of such fines, but it does represent a cost factor to convert the fines to useable absorbent clay granules. However, the relatively few deposits geographically of the most desirable absorptive clay minerals pose the principal problem for this adds materially to cost in shipping packaged material, or shipping such materials in the bulk, over long distances to the principal markets for such absorbent clay granules.
The need for such absorbents of the character of the present invention is worldwide, and the greatest need is in industrial, agricultural, and urban areas. Many of these areas are far removed from the sources of sorptive minerals such as absorbent clay, and the resulting problems have created hurdles for some time that the industry must surmount if it is to satisfy in an acceptable manner the needs of industry and agriculture, as well as those for the animal pet boxes.
Efforts have long been made to find an acceptable synthetic substitute more readily available to the principal markets for the most desirable clay absorbents, but until the invention of the process and product of the Been application referred to above such efforts have been unsuccessful. The synthetic absorbent granules of the Been application identified above, and those of the present invention, which is an improvement over the Been invention, both utilize a commercial type gypsum plaster which is rehydrated to gypsum. Gypsum plaster of a commercial type is available in commercial, urban, and agricultural areas, and the present invention is practiced with equally available equipment. Hence, the invention can be practiced in many areas in the world to provide a useful absorbent product without incurring excessive transportation costs.
Before providing a summary description of the present invention, certain words and phrases will be explained for their meaning as used in this application.
"Agricultural chemicals" as used herein means pesticides, herbicides, insecticides and the like for which the synthetic granular absorbent of the product invention acts as a carrier in the sense that word is commonly used in this art. A particular agricultural chemical (or chemicals) in whatever form and in whatever way it is combined with synthetic granular material, is distributed in different conventional means by spreading, or by otherwise applying such material to the weeds, crops, and the like to be affected.
"Aridization" as a property of the commercial gypsum plasters used in the practice of the present process, and as used herein, means the step in processing the naturally occurring gypsum rock when calcium chloride salt is introduced into the water demand of the plaster resulting from the calcination.
"Balls", and "granules" have the same general meaning herein, and each word identifies the liquid absorbent material manufactured by the present process. "Granule" is defined as a small particle, but in this application to distinguish the minute dry powdered plaster pieces, the word "particle" is used herein for the latter.
"Density", or "bulk density" as related to the synthetic absorbent of the present invention is a factor from the standpoints of weight and volume in packaging such products, and is an equally important factor in the use of such synthetic granules as carriers for agricultural chemicals. This property affects the weight and volume of material which goes into a bag or package of a predetermined size for accomodating the volume printed on the bag or package. Weight and volume of the granules represented in the carrier material are also important in the loading and in the operation of the spreading equipment for such carrier material. Furthermore, with respect to such synthetic granular absorbent, the lower the density the higher the absorptive capacity thereof, so that density is an important factor with respect to absorptive capacity which is the characteristic that must be obtained in the synthetic material manufactured.
"Consistency" means a measurement of the water carrying capacity of the plaster or calcium sulfate hemihydrate.
"Liquid" and "moisture" are used interchangeably herein, because that to be absorbed by the product of the present invention may represent a problem with a strict definition for each word and "moisture" is liquid although possibly diffused or condensed.
"Stucco" as the name of material processed by the present invention is synonomous with "plaster" so far as the present process is concerned.